A touch input system, as the name suggests, senses contact as an input. The contact may be a physical touch (i.e., physical contact) or a proximate touch (i.e., no physical contact, such as hovering). A touch input system may include a touch screen display and a touch controller. The touch screen display may include a display layer configured to display information and a sensing layer configured to sense a touch input on the touch screen display, for example, using one or more of a resistive, capacitive and surface wave sensing technology. The sensing layer may include a plurality of sensors connected to the touch controller.
The touch controller is generally responsible for detecting touch events on the basis of signals received from the touch screen display and reporting those touch events as touch reports to a host. A touch report may include the location of the touch event (e.g., X, Y coordinates), pressure, touch gestures, and/or other attributes output by the touch controller. A criteria for evaluating the touch controller is its latency, which generally refers to the delay between a touch input on the touch screen display and when a corresponding touch event is reported to the host via electrical signals as a touch report.
The touch controller latency may be measured as an initial latency (also known as “touch-down latency”) or a continuous latency (also known as “panning latency”). Initial latency is measured from the time when a first touch input occurs to when a corresponding touch event is detected. Thus, the measured initial latency may include a wakeup time of the touch controller. Continuous latency, on the other hand, measures the ongoing time it takes the touch controller to process subsequent touch inputs after the first touch input. That is, the measured continuous latency represents how responsive the touch controller is to changing touch inputs.
Determining the continuous latency of a touch controller is important because it impacts the overall responsiveness of a device in which the touch input system is incorporated. However, manufacturers of touch controllers generally do not specify the touch controller latency. Furthermore, measuring continuous latency is challenging because it is often difficult to correlate a specific touch input to a corresponding touch report issued by the touch controller. As such, there exists a need for a system and method of measuring continuous touch controller latency that overcome these problems.